Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.95	9.107%	$93.7775	$93.78	$93.80	$93.80
Purchase #2	$80.81	11.174%	$89.8397	$89.84	$89.85	$89.80
Purchase #3	$129.43	13.231%	$146.5549	$146.55	$146.55	$146.60
Purchase #4	$30.34	5.209%	$31.9204	$31.92	$31.90	$31.90
Purchase #5	$18.93	4.624%	$19.8053	$19.81	$19.80	$19.80
Purchase #6	$246.45	11.617%	$275.0801	$275.08	$275.10	$275.10
Purchase #7	$7.31	3.687%	$7.5795	$7.58	$7.60	$7.60
7 purchase totals =	$599.22		$664.5574	$664.56	$664.60	$664.60